Defects in pyruvate kinase cause a conditional increase of thiamine synthesis in Salmonella typhimurium

As genomic sequence data become more prevalent, the challenges in microbial physiology shift from identifying biochemical pathways to understanding th e interactions that occur between them to create a robust but responsive me tabolism. One of the most powerful methods to identify such interactions is in vivo phenotypic analysis. We have utilized thiamine synthesis as a mode l to detect subtle metabolic interactions due to the sensitivity allowed by the small cellular requirement for this vitamin. Although purine biosynthe sis produces an intermediate in thiamine synthesis, mutants blocked in the first step of de novo purine biosynthesis (PurF) are able to grow in the ab sence of thiamine owing to an alternative synthesis. A number of general me tabolic defects have been found to prevent PurF-independent thiamine synthe sis. Here we report stimulation of thiamine-independent growth caused by a mutation in one or both genes encoding the pyruvate kinase isozymes. The re sults presented herein represent the first phenotype described for mutants defective in pykA or pykF, and thus identify metabolic interactions that ex ist in vivo.